import "server-only";

import { cookies, headers } from "next/headers";
import Negotiator from "negotiator";
import { match } from "@formatjs/intl-localematcher";
import type { Locale } from ".";
import { i18n } from ".";

export const getLocaleOnServer = (): Locale => {
  // @ts-expect-error locales are readonly
  const locales: string[] = i18n.locales;

  let languages: string[] | undefined;
  // get locale from cookie
  const localeCookie = cookies().get("locale");
  languages = localeCookie?.value ? [localeCookie.value] : [];

  if (!languages.length) {
    // Negotiator expects plain object so we need to transform headers
    const negotiatorHeaders: Record<string, string> = {};
    headers().forEach((value, key) => (negotiatorHeaders[key] = value));
    // Use negotiator and intl-localematcher to get best locale
    languages = new Negotiator({ headers: negotiatorHeaders }).languages();
  }

  // match locale
  const matchedLocale = match(languages, locales, i18n.defaultLocale) as Locale;
  return matchedLocale;
};
